The South American catfish genus Auchenipterichthys has been revised by scientists and four species have been redescribed.
Carl J. Ferraris Jr., Richard Vari and Sandra Raredon looked at the auchenipterid genus and found that it contained four species: Auchenipterichthys thoracatus; A. coracoideus; A. longimanus and A. punctatus.
Their paper, which is published in the latest edition of the journal Neotropical Ichthyology, says that A. thoracatus, which was previously considered to be widely distributed along the Amazon basin is, in fact, restricted to the Rio Madeira.
In other parts of the Amazon basin, another Auchenipterichthys species, A. coracoideus, has been mistakenly identified as thoractus. This one is most commonly known from the upper reaches of the Rio Essequibo.
In contrast, A. longimanus, is indeed a widely distributed species and occurs over most of the Amazon and Orinoco drainage.
The fourth one, A. punctatus, is found in the central Amazon region, particularly around the upper Rio Negro and Rio Orinoco.
There's a key to the genus in the paper to aid their identification.
For more details see the paper: Ferraris, CJ., Vari, RP., Raredon, SJ. (2005) - Catfishes of the genus Auchenipterichthys (Osteichthyes: Siluriformes: Auchenipteridae) a revisionary study. Neotropical Ichthyology. 3 (1): 89-106.